The present invention relates to an optical system for illumination (lighting system) for applying an illuminating light to a light bulb such as a liquid crystal or DMD (Digital Micromirror Device) and a projection type display unit using the same, and more particularly to an optical system for illumination (lighting system) for a projection type display unit that is excellent in the illumination uniformity, and has a high light utilization efficiency, and the projection type display unit using this optical system for illumination (lighting system).
In recent years, a projector device (projection type display unit) as an image display device of large screen has drawn a good deal of public attention.
A CRT projector device using a high definition and high luminance CRT of small size, a liquid crystal projector device using a liquid crystal panel, and a DMD projector device using a DMD (Digital Micromirror Device) have been manufactured.
Various products not only coping with the AV sources such as movies or TV programs, but also belonging to a category called a data projector for projecting the computer image, have extended rapidly the market. The remarkable improvements of performance including the enhanced brightness or contrast, higher resolution, and more uniform brightness of the projection screen, have been made.
Particularly, a projector device using a light bulb such as the liquid crystal or DMD is superior to a CRT projector device in the respect of capability of enhancing the brightness and resolution independently, and has been more applied to the projection television (rear projection type projector).
The conventional light bulb optical system for illumination (lighting system) typically relies on a Koehler illumination method of one kind in which a light bulb is arranged and illuminated in the optical path of a lens system in a conjugate relation between a light source and an exit pupil of a projection lens.
However, to improve the illumination uniformity in recent years, a fly-eye integrator method or a rod integrator method has been mostly employed, and an image forming performance at higher level and a more intricate constitution have been required for the optical system for illumination (lighting system).
FIG. 17 shows a conventional reflection type projector as disclosed in Japanese Patent No. 2939237.
In the figure, reference numeral 110 denotes alight source for generating and emitting a light; reference numeral 120 denotes a color wheel for selectively transmitting the light emitted from the light source 110 with the wavelength; reference numeral 130 denotes light mixing means (light mixing element) for diverging/converging or irregularly reflecting the light incident from the light source 110 into the uniform light; reference numeral 140 denotes a relay lens unit for converging the incident light into the parallel light; reference numeral 150 denotes a critical angle prism for reflecting the light reflected and incident again from image generating means 160; and reference numeral 170 denotes a projection lens unit for enlarging and transmitting the incident light to be directed toward a screen.
As a specific example of the light mixing means 130, a scrambler 135 is arranged in the figure.
Reference numerals 135a and 135b denote a plane of incidence and a plane of emergence for the scrambler 135, respectively. At a point to which a light emitted from a lamp 111 of the light source 110 is converged, the plane of incidence 135a perpendicular to the optical path is arranged. This plane of incidence 135a, the plane of emergence 135b perpendicular to the optical path and four lateral faces form a rectangular parallelepiped.
An aspect ratio of the plane of emergence 135b results in a rectangle corresponding to that of an FLCD (Ferroelectric Liquid Crystal Display) constituting the image generating means 160.
A nonuniform light from the light source 110 is mixed into the uniform light by the scrambler 135, and emitted from the plane of emergence 135b. 
The relay (transmission) lens unit 140 is composed of a convergent lens 141 for diverging this uniform light, and a collimator lens 143 for converging the incident divergent light into the parallel light. This parallel light illuminates the FLCD 163.
With this conventional constitution, a reflection type projector can be provided in which the critical angle prism 150 is employed to transform a proceeding path of light, without the use of a polarizing beam splitter, and the arrangement of optical axes for the optical system can be easily made without need of a long optical length.
The critical angle prism 150 is not described in detail here, but has a lot of problems with degrading the resolution of a projected image, easily causing an unnecessary ghost light, and increasing the costs owing to significant difficulties in the manufacture, except for an action of separating optically and physically the optical system for illumination and the optical system for projection.
In the case where the critical angle prism 150 is not employed, there is the high possibility of bringing about the problem with physical interference between the optical system for illumination and the optical system for projection.
In the conventional examples, an instance was disclosed in which a DMD was employed as the image generating means, but when the DMD is employed, the interference problem can not be mostly avoided.
The DMD acts to modulate an incident light flux on the basis of the image information by changing the tilt of a micromirror to select a reflecting direction of the incident light.
Hence, the incident angle of rays illuminating the DMD is limited, causing interference between the optical system for illumination and the optical system for projection.
FIG. 18 is a perspective view illustrating the constitution of two pixels of DMD.
In the figure, reference numerals 510, 511 denote micromirrors, which are tilted by +10 degrees and xe2x88x9210 degrees from the normal of an element 500, respectively.
For more details of the DMD, see Larry J. Hornbeck, xe2x80x9cDigital Light Processing for High-Brightness, High-Resolution Applications.xe2x80x9d SPIE Vol.3013, pp.27-40. The DMD will not be described in any detail.
In order to illuminate the DMD, the ray of light must be incident from a direction inclined at a certain angle from the normal of the DMD, as will be apparent from the operation of the micromirror.
The micromirror is tilted at an angle of xc2x110 degrees, and the rotational axis of the micromirror is directed at 45 degrees toward the square micromirror. Therefore, in the case where a reflected light is directed in a normal direction of the DMD, an illuminating light must be made incident from a direction inclined by 20 degrees from the normal and with an azimuth of 45 degrees.
FIG. 19 is a schematic view illustrating part of an optical system employing the DMD as image generating means, wherein the physical interference between the optical system for illumination and the optical system for projection is described in the case where the critical angle prism is not used.
In the figure, reference numeral 440 denotes a final lens of the optical system for illumination; reference numeral 441 denotes a lens-barrel of the final lens 440; reference numeral 512 denotes a DMD; reference numeral 70 denotes an optical axis of illumination; reference numeral 71 denotes an optical axis of projection; reference numeral 80 denotes a projection lens; and reference sign xcex1 denotes an admission angle of the ray of beam on the DMD 512, or an angle made between the optical axis of illumination 70 and the normal of the DMD 512.
The projection lens 80 is placed in the front of the DMD 512, and is supposed to be a post diaphragm type in the figure.
In the case where the tilt of the micromirror for the DMD 512 is xc2x110 degrees, the incident angle of the ray of light onto the DMD 512 must be xcex1=20xc2x0, leading to the high possibility that the physical interference may arise in the vicinity of a section circled by the dotted line in the figure.
In this case, a part of the illuminating light flux or projecting light flux is intercepted, and the illumination or projection performance may be sacrificed.
In order to avoid such an inconvenience, it was required to reduce an incident aperture diameter of the projection lens, or delete part of the lens-barrel intentionally, for example.
However, since these are factors of causing the poor performance of the projection lens or the increased costs, in practice a method is often taken of shifting the optical axis of the projection lens with respect to the central axis of the DMD by a predetermined amount, as shown in FIG. 20. Note that the same numerals indicate the same or like parts as in FIGS. 19 and 20. The same parts are not described.
If the optical axis is shifted, the projecting direction of a projector device becomes upward from the device, and this technique is positively employed in the case of a front projector.
Of course, it is necessary that the incident angle of the illuminating light with respect to the normal of the DMD may be made a larger angle xcex2 by a shift amount of the projection lens 80. Further, a large image circle of the projection lens 80 must be designed than in a case of FIG. 19.
However, in the system in which the inclination of the projecting direction is not permissible, the problem of interference is difficult to avoid, and a method of placing the critical angle prism was adopted, for example, resulting in the increased cost.
The present invention has been achieved to solve the above-mentioned problems, and it is an object of the invention to provide an optical system for illumination (lighting system), and a projector device (projection type display unit) using the optical system for illumination (lighting system), by directing an illuminating light flux to a reflective type light bulb represented by a DMD, without the use of expensive optical elements such as a critical angle prism, wherein there is no significant effect on the illumination performance, particularly the illumination uniformity, even if the illuminating light flux is partly intercepted.
According to the present invention, there is provided a lighting system comprising converging means for converging a light emitted from an illuminant and forming a converged image of the illuminant at a predetermined position, a light mixing element for having an end face of incidence near the position at which the converged image of the illuminant is formed, and reducing an irregular luminance of the converged image of the illuminant incident on the end face of incidence to form a uniform light source face on an end face of emergence, and an optical system for transmission for directing an illuminating light flux from the plane of light emergence onto the illuminated face side of a light bulb in a non-telecentric state, a first lens group and a second lens group being arranged in order from the light mixing element side to the illuminated face side of the light bulb, in which a first optical conjugate relation exists between the end face of incidence of the light mixing element and a virtual face at a position of a diaphragm disposed in the vicinity of a lens means final face closest to the illuminated face constituting the second lens group in terms of the first lens group and the second lens group, and a second optical conjugate relation exists between the end face of emergence of the light mixing element and the illuminated face.
In the lighting system according to the invention, the second lens group of the optical system for transmission is comprised of a meniscus lens having a negative refracting power with a convex face directed toward the light mixing element, and a lens having a positive refracting power, which are arranged in order from the light mixing element side.
In the lighting system according to the invention, the first lens group of the optical system for transmission consists of one positive lens and the second lens group consists of two positive lenses.
In the lighting system according to the invention, the light mixing element is shaped like a hollow cylinder formed by folding a single reflective member.
In the lighting system according to the invention, at least one of the first lens group and the second lens group of the optical system for transmission is a concave mirror or a convex mirror.
A projection type display unit according to the invention comprises a lighting system according to any one of aspects 1 to 5, a light bulb having a great number of pixels in a two-dimensional array structure that are illuminated by a light flux in a non-telecentric state that is emergent from an optical system for transmission of the lighting system, and that are driven independently of each other, and projection lens means for projecting the light emergent from the light bulb onto screen means.
In the projection type display unit according to this invention, an optical system for transmission in a lighting system has a first lens group and a second lens group arranged in order from the light mixing element side to the illuminated face side of a light bulb, the first lens group consisting of at least one meniscus lens having a positive refracting power, and the second lens group consisting of first lens means having a negative refracting power and second lens means having a positive refracting power in a region from the light mixing element side to the illuminated face side of the light bulb, the first lens means and the second lens means being arranged in order from the light source side, in which an illuminating light flux is made emergent in a non-telecentric state from the optical system for transmission, and a relation
0.68 less than f1/f0 less than 0.76 
is satisfied, where the focal length of an overall optical system for transmission is f0 and the focal length of the first lens group is f1.
In the projection type display unit according to the invention, a lighting system has a rotary color filter arranged immediately before or after the light mixing element.